Crankcase gases from internal combustion engines contain oil in the form of an oil mist or oil droplets mixed with other impurities such as soot and hydrocarbons. Such impurities in the crank-case gases may form sticky substances. Furthermore, it is common to add various additives to the oil of the internal combustion engine in order to improve the properties of the oil for the lubrication and cooling of the internal combustion engine. However, such additives may have a negative effect due to the fact that the impurities, such as soot and hydrocarbons, form substances that are even more sticky.
The purpose of the centrifugal separator disclosed in WO 2004/022239 is to improve the lubrication of an upper bearing supporting the hollow spindle of the centrifuge rotor. The oil is conveyed through the hollow spindle and an upper opening to a small chamber from where the oil is conveyed through the upper bearing into the inlet to be mixed with the crankcase gases. A relatively small amount of oil is needed for the lubrication of the upper bearing. The opening of the hollow spindle of the centrifugal separator disclosed in WO 2004/022239 is configured to supply only such a relatively small quantity of oil sufficient for the lubrication of the upper bearing only. This prior art thus aims at keeping the quantity of oil supplied at a minimum.
One problem of the centrifugal separator disclosed in WO 2004/022239 and other prior art centrifugal separators for cleaning of crankcase gases is that the oil and impurities contained in the crankcase gas is very sticky, as mentioned above, so that sticky agglomerations of soot and impurities may attach to the inner parts of the centrifugal separator, especially the inner wall surface of the stationary casing.
WO 2009/029022 discloses another centrifugal separator for cleaning a gas containing liquid and solid impurities. The centrifugal separator of this prior art document comprises a supply device for supplying an aerosol through a nozzle into the inlet channel of the centrifugal separator. The aerosol, which may be formed by water, has the purpose of preventing the impurities from attaching to the separation discs.
WO 2005/087384 discloses another centrifugal separator for cleaning a gas. This centrifugal separator comprises a flushing nozzle arranged to supply a cleaning liquid for flushing the separation discs.